how????

Hairdryer (not heatgun) and spatula...and elbow grease!

super hyper duper easy
[1] remove the pad by rolling it underthumb
[2] put a cloth on the glue left
[3] imbibate with a solvent (I use "Solvent F"). never use acetone, it creates micro cracks in the resin, and cover with a plastic sheet
[4] let the solvent marinate 15mn
[5] remove cloth, and scrape the glue with an (old) credit card, the glue cames off as easy as a butter layer

Images in: http://www.gongsup.com/forum/viewtbroke://www.gongsup.com/forum/viewtopic.php?p=46244#p46244opic.php?p=46244#p46244

I did this 2 month ago to remove a 25cm square patch around a handle to repair it, and also on the tail section of a 2nd hand board to add a tail pad. I did nothing special, just put the solvent layer ins the cut out, covered and removed. The remaining pad didnt seem to get off, I took care not to push/pull on on while wet, I guess once the solvent dries out it is as well stuck as before.

Note that some factory-set pads may be harder to remove, if they are glued with epoxy resin. But I don't think this method is used anymore.